2D and 3D Polar Plume Analysis from the Three Vantage Positions of STEREO/EUVI A, B, and SOHO/EIT

Polar plumes are seen as elongated objects starting at the solar polar regions. Here, we analyze these objects from a sequence of images taken simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and SOHO/EIT. We establish a method capable of automatically identifying plumes in solar EUV images close to the limb at 1.01 - 1.39 R in order to study their temporal evolution. This plume-identification method is based on a multiscale Hough-wavelet analysis. Then two methods to determined their 3D localization and structure are discussed: First, tomography using the filtered back-projection and including the differential rotation of the Sun and, secondly, conventional stereoscopic triangulation. We show that tomography and stereoscopy are complementary to study polar plumes. We also show that this systematic 2D identification and the proposed methods of 3D reconstruction are well suited, on one hand, to identify plumes individually and on the other hand, to analyze the distribution of plumes and inter-plume regions. Finally, the results are discussed focusing on the plume position with their cross-section area.

💡 Research Summary

The paper presents a comprehensive methodology for the automatic detection and three‑dimensional reconstruction of solar polar plumes using simultaneous observations from the three EUV imagers STEREO‑EUVI A, B and SOHO‑EIT. The authors focus on a one‑month interval (1 Nov – 1 Dec 2007) during solar minimum, when plumes are most clearly visible in the 171 Å Fe IX line. After standard calibration (secchi_prep, eit_prep) the images are cleaned of cosmic‑ray hits with a 5‑pixel median filter applied three times. A simple background model is built from the minimum of a 30‑day window, and a contrast‑enhancement operation (I‑B)/B is applied to highlight the faint plume structures while preserving photometric integrity.

The core detection algorithm is a multiscale Hough‑wavelet transform. Traditional Hough analysis maps straight lines to points in (θ, ρ) space, but it does not account for finite width. By convolving the image with a family of Mexican‑Hat wavelets that are translated (ρ), rotated (θ) and dilated (scale a), the authors obtain a three‑dimensional response H(ρ,a,θ). For each (ρ,θ) the scale a that maximizes the response is identified (a_M), providing an estimate of the plume’s cross‑sectional width (σ≈a_M/√2). Synthetic tests with Gaussian‑shaped plumes confirm that the response scales as A/σ, where A is the plume intensity, and that narrower plumes produce stronger peaks. Applied to the real data, the solar polar region is remapped to cylindrical coordinates (r, φ) and limited to φ∈